Naked Science Forum
Non Life Sciences => Technology => Topic started by: neilep on 28/01/2012 18:19:52
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Dearest Microwaveovenologists,
As a sheepie I of course love microwave ovens ....Oh yes indeed !...If Neil Armstrong had just pondered his words for a few more seconds and said "it's one small step for man, one giant leap for microwave ovens" instead...Just imagine what a fantastic world we could live in by now ! *le sigh*
It scares me the repercussions ever since !!
Anyway.......setting aside that extraordinary missed opportunity can you help me with a kweschun ?
You see, at work we have not one ..but two !!....Yep...you read that right....shocking and awe making though it may be....Two microwave ovens ! OMG !!....you can take your 120million pound euro lottery prize and shove it !!...we have two microwave ovens at work so there !!...nyahh nyahh nyahh nyahh !!
One is a regular consumer one and the other is a commercial one. I would at this juncture post a photo but I'm not working today and the zoom on my phone camera is just not capable enough of producing the required image.
The Consumer one has the usual spinny glassy thing inside but the commercial one does not....it just has a flat surface to place your nutritional yumminess onto.
Why's that then ?...Why Doesn't A Commercial Microwave Have A Spinny Thing Inside ?
Go on....you can tell me !!..it's just you and I....I won't tell...I'm good at keeping seekrits !
hugs and shmishes
mwah mwah mwah
Neil
[ Invalid Attachment ] It's a ' Micro ' wave !!..*le groan*
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Some microwave ovens rotate the aerial (microwave source) rather than the food. One of the problems is that the microwaves form standing waves inside the oven so unless you either move the food or the aerial, you can get parts of the food that don't heat properly. I expect the commercial one is of the rotating aerial type.
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First generation home microwaves did not have the rotating table.
And, the rotating platform in my current microwave wore out a few years ago... and it seems to work just fine without the food spinning.
My guess is that the commercial microwaves have fewer moving parts to go bad. However, the interpretation of moving the beam (or perhaps mirror) would make it easier to keep the microwave cleaner, with fewer things that can be broken by the end user. And a spinning mirror, or set of mirrors would have very little wear and tear.
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Some microwave ovens rotate the aerial (microwave source) rather than the food. One of the problems is that the microwaves form standing waves inside the oven so unless you either move the food or the aerial, you can get parts of the food that don't heat properly. I expect the commercial one is of the rotating aerial type.
Is that true? The standing waves should form because of the geometry of the cavity (they bounce back and forth between two parallel walls of the box). You shouldn't be able to generate new standing wave patterns without changing the geometry of the box, so moving the magnetron around wouldn't help, I would think...
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Ah--- a bit of searching turned up the part called a "stirrer." In microwaves, the magnetron sits still, but there are often fans located inside the microwave cavity. These fans disrupt the standing wave pattern as the waves bounce off them, leading to a much more even distribution of microwaves and fewer "hot spots." I'm guessing commercial ovens have a lot fancier stirrers.
So breaking up standing wave patterns is key if you don't want to rotate your food.
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It's not the standing waves that are the problem, it's the standing around waiting for your meal to cook that is.
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So the rotating tray inside of a microwave is likely a lot like the dummy antennas on telephones in the past.
The dummy antennas were installed because people thought that the bigger antennas meant the phones were more powerful, when in fact, they did nothing.
Likewise, a rotating tray inside of the microwave doesn't mean a better microwave, but likely is an indicator of a poorly designed microwave.
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Oh, I don't think anyone is saying the spinny thing does not work. It should work because it moves the item so that the standing wave nodes are not constant relative to the thing that is being heated.
I think there is a TNS experiment that reveals the nodes in a static lump of butter. If the butter is on a spinny thing, the butter should be heated uniformly, and the nodes will not be revealed.
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beaten too it again -
The experiment I have seen uses a (plain therfore homogeneous) chocolate bar rather than butter (my experience of microwaving butter to make perfect toast in the morning is that it tends to melt internally and after a very short time) to determine the speed of light/ EM radiation.
Broadly this is done, by removing the revolving plate, carefully microwaving the chocolate bar and seeing where the soft spots in the chocolate form. By measuring the centres (multiplying by 2 to estimate one wave length) and multiplying by the frequency (shown on the manufacturers plate on the back/ underside of the device) you can get a reasonable kitchen science estimate of c.
However if you put the chocolate bar (on a saucer) in the commercial unit I am sure that it will melt (relatively) evenly suggesting that there is a "stirer"(as suggested) or some other trickery tucked away to ensure even cooking.
So get out the dairy milk and get zapping (pictures or it did not happen)